De Broglie

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De Broglie

  1. 2. Louis De Broglie (1924) <ul><li>French physics graduate student </li></ul><ul><li>Proposed idea that accounted for the fixed energy levels in Bohr’s model </li></ul>
  2. 3. If waves can have particle like characteristics, then can particles, such as electrons, have wave like characteristics???
  3. 4. What he knew… <ul><li>Electrons have wavelike motion (because it’s a particle) </li></ul><ul><li>An electron had restricted orbits </li></ul><ul><li>Each orbit had a fixed radius from the nucleus </li></ul><ul><li>Are a wide variety of wavelengths, frequencies, and energies possible? </li></ul>
  4. 6. <ul><li>No…there could only be allowed certain possible frequencies, wavelengths, and energies in an atom </li></ul><ul><li>De Broglie came up with an equation for the wavelength of a particle of mass (m) moving at velocity (v). </li></ul>
  5. 7. De Broglie’s Equation
  6. 8. What does this equation do? <ul><li>What are we using? </li></ul><ul><ul><li>Wavelength </li></ul></ul><ul><ul><li>Planck’s constant </li></ul></ul><ul><ul><li>Mass of the particle </li></ul></ul><ul><ul><li>Velocity </li></ul></ul><ul><li>Tells us that all moving particles have wave-like characteristics </li></ul>
  7. 9. Food for thought… <ul><li>Cars? </li></ul><ul><li>Baseball? </li></ul><ul><li>Do these have wavelike characteristics? Why or why not? </li></ul>
  8. 10. <ul><li>Yes…let’s look at the equation… </li></ul><ul><li>λ = h </li></ul><ul><li>mv </li></ul><ul><li>The car and the baseball do have a velocity and a mass… </li></ul><ul><li>Using De Broglie’s equation we do get a wavelength for the movement of a baseball and a car… </li></ul><ul><li>Let’s try the calculation… </li></ul>
  9. 11. Problem time… <ul><li>Mass of car= 910 kg </li></ul><ul><li>Velocity of car= 25m/s </li></ul><ul><li>What is the wavelength of the moving car? </li></ul><ul><ul><li>2.9 x 10^-38 m </li></ul></ul><ul><li>How big is this? </li></ul><ul><li>Can we see or measure this wavelength? </li></ul><ul><ul><li>No, much to small to be detected, even with the most sophisticated equipment </li></ul></ul>
  10. 12. Another one… <ul><li>Electron speed= 25 m/s </li></ul><ul><li>Electron mass= 9.11 x 10^-28 g </li></ul><ul><li>What is the wavelength of the moving electron? </li></ul><ul><ul><li>2.9 x 10^-5 m </li></ul></ul><ul><li>Do you think we can measure this wavelength and see it? </li></ul><ul><ul><li>Yes, with the right equipment </li></ul></ul>
  11. 13. Practice makes perfect  <ul><li>What is the wavelength of an electron of mass 9.11 x 10-28 kg traveling at a velocity of 2.00 x 108 m/s? (Planck's constant = 6.63 x 10-34 J/Hz. </li></ul><ul><li>3.64 x 10-15m. </li></ul>

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